In order to achieve an effective closing, a fixed valve element commonly referred to as a fixed valve plate, and a movable valve plate of the mixing valve must be pressed against each other with a compressive force greater than the force exerted by the pressure of the flowing water because, otherwise, the water pressure would separate the movable valve plate from the fixed valve element preventing them to be closed, and similarly a compressive force must be applied between the fixed valve plate and its own support surface so as to compress a seal therebetween either to assure proper function of the seal or to prevent an ejection of the seal itself or its deformation in case excessive pressures should occur.
In most cases, the minimum compressive force necessary to compress the seal and to hold it tightly in its correct position is much higher than the minimum compressive force necessary to keep the fixed valve plate and the movable valve plate in operative contact. In known cartridge valve structures, the fixed valve plate is simply resting on a support seat in a bottom portion of a replaceable cartridge inside the faucet body and a compressive force is exerted between the movable valve plate and support seat which pushes the support seat toward the movable valve plate or vice versa.
As a consequence, the exerted compressive force must be at least equal to or greater than the higher one of the two minimum compressive forces needed for the specified purposes. In other words, the applied compressive force is equal to the compressive force necessary to compress the seal and hold it tightly in its correct position. The compressive force is thus unnecessarily high for the purpose of keeping the movable valve plate in contact with the fixed valve plate. Because of such excessively high force applied between the movable plate and fixed plate, the faucet is harder to operate and needless mechanical stresses of the parts are introduced. A cartridge valve in which its bottom portion is hydraulically biased to produce a compressive force between the fixed valve plate and movable valve plate are particularly disadvantaged by the above mentioned excessively high compressive forces.